1. Field of the Invention
The present invention relates to a cooling device using a liquid refrigerant and a method for manufacturing the cooling device. The present invention also relates to portable equipment including the cooling device.
2. Description of Related Art
A conventionally known cooling device using a refrigerant is described by JP 2001-24372 A.
FIG. 17 is a schematic perspective view showing how elements of a cooling device are arranged in a conventional notebook personal computer (in the following, referred to as a xe2x80x9cnotebook PCxe2x80x9d) in which the cooling device is incorporated.
In FIG. 17, numeral 101 denotes a housing of the notebook PC, numeral 102 denotes a heat generator such as a central processing unit (CPU), numeral 104 denotes a heat absorber, numeral 103 denotes a heat-transfer pad arranged between the heat generator 102 and the heat absorber 104, numeral 105 denotes a pump, and numeral 106 denotes a heat radiator. Numeral 107 denotes a display portion of the notebook PC, and numeral 108 denotes a flow channel that allows communication between the interiors of the heat absorber 104, the pump 105 and the heat radiator 106. Inside the flow channel 108 is filled with a water-based or fluorocarbon-based liquid refrigerant.
Next, the operation of this cooling device will be described.
When the notebook PC is used, the pump 105 is powered and activated so as to send out the liquid refrigerant by pressure, whereby the liquid refrigerant circulates through a closed-loop circulating cycle from the pump 105, the heat absorber 104, the heat radiator 106 to the pump 105, which are connected via the flow channel 108. Thus, the liquid refrigerant pushed out from the pump 105 absorbs heat from the heat generator 102 in the heat absorber 104, moves to the heat radiator 106 to radiate the heat and be cooled down again and then returns to the pump 105. By repeating this operation, the heat generated in the notebook PC is radiated outward.
When this cooling device is used for a long time, the liquid refrigerant is heated and cooled, so that a gas (bubbles) is generated in the device. In particular, considerable gas generation occurs inside the heat absorber 104. Since the generated gas blocks the flow channel in the heat absorber 104, a channel resistance increases considerably, thus deteriorating flow rate characteristics of the pump 105. As a result, the flow velocity of the liquid refrigerant drops, causing a problem that a cooling power deteriorates.
Furthermore, inside the heat absorber 104, the formation of a gas layer between an inner wall of the heat absorber 104 and the liquid refrigerant lowers heat conductivity. Consequently, there has been a problem that lowering heat absorbing power of the heat absorber 104 deteriorates the cooling power of the cooling device.
In addition, since not only the liquid refrigerant but also the generated gas flows into other devices, for example, the pump 105, the performance of the pump 105 declines, leading to a problem that the cooling power deteriorates.
It is an object of the present invention to solve these problems and to provide a cooling device that maintains an excellent cooling effect even after a long time use, and a method for manufacturing the cooling device. It is a further object of the present invention to provide portable equipment that achieves an improvement in performance owing to a stabilized cooling power.
In order to achieve the above-mentioned objects, the present invention has the following configurations.
A first cooling device according to the present invention includes a pump, a heat absorber, a heat radiator, a flow channel that allows communication between interiors of the pump, the heat absorber and the heat radiator and forms a closed-loop circulating cycle therebetween, and a liquid refrigerant that circulates in the flow channel. A volume of a gas generated in the liquid refrigerant owing to temperature change within an operating temperature range of the liquid refrigerant is smaller than a volume of a sphere that is inscribed in a cross-section of the flow channel.
A second cooling device according to the present invention includes a pump, a heat absorber, a heat radiator, a flow channel that allows communication between interiors of the pump, the heat absorber and the heat radiator and forms a closed-loop circulating cycle therebetween, and a liquid refrigerant that circulates in the flow channel. A difference between a product described below and an amount of a gas dissolved in the liquid refrigerant in a state where no gas is generated is smaller than a volume of a sphere that is inscribed in a minimal cross-section of the flow channel. The product is a product of a minimal solubility of the gas in the liquid refrigerant within an operating temperature range of the liquid refrigerant and a total capacity (volume) of the flow channel.
A first method for manufacturing a cooling device according to the present invention is a method for manufacturing a cooling device including a pump, a heat absorber, a heat radiator, a flow channel that allows communication between interiors of the pump, the heat absorber and the heat radiator and forms a closed-loop circulating cycle therebetween, and a liquid refrigerant that circulates in the flow channel. The method includes sealing the liquid refrigerant in the flow channel while maintaining an atmosphere at a temperature at which a gas solubility in the liquid refrigerant takes on a minimal value within an operating temperature range of the liquid refrigerant or is smaller than the minimal value.
A second method for manufacturing a cooling device according to the present invention is a method for manufacturing a cooling device including a pump, a heat absorber, a heat radiator, a flow channel that allows communication between interiors of the pump, the heat absorber and the heat radiator and forms a closed-loop circulating cycle therebetween, and a liquid refrigerant that circulates in the flow channel. The method includes sealing the liquid refrigerant in the flow channel under an atmosphere decompressed so that a gas solubility in the liquid refrigerant at a temperature of an atmosphere at the time of sealing the liquid refrigerant in the flow channel is smaller than a minimal value of the gas solubility under an atmospheric pressure within an operating temperature range of the liquid refrigerant.
According to the first and second cooling devices and the first and second manufacturing methods of the present invention described above, even when the solubility changes due to rapid heating or cooling of the liquid refrigerant, no gas is generated. Thus, it is possible to prevent the cooling power from deteriorating due to the deterioration in flow rate characteristics of the pump occurring because the gas generated after a long time use blocks the flow channel, the lowering of heat conductivity caused by adhesion of the gas to the inner wall of the flow channel and the decline in the pump performance occurring because the generated gas flows into the pump. As a result, a cooling device that maintains an excellent cooling efficiency even after a long time use can be provided.